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OCVR : Ocean Carbon Variational Reanalyzer - System The ocean plays a crucial role as it contributes to an uptake of about a quarter to a third of the anthropogenic emissions with significant year to year variations (Sabine et al., 2004). For the CARBONES CCDAS, we have developed a statistical model to estimate air-sea fluxes from satellite, in-situ measurements and model outputs. The fluxes rely deeply on the sea surface carbon partial pressure estimated in a first step by the OCVR system described below. 1) Model description Importance of the ocean surface carbon dioxide partial pressure (PCO2sw) The air-sea CO2 flux is typically controlled by two terms embedded in the formula : F = (k α) . ΔpCO2 where k is the piston velocity, α is the solubility (Weiss, 1974) and ΔpCO2 the difference between the pCO2 in surface seawater and that in the overlying air. ΔpCO2 represents the thermodynamic driving potential for the exchange flux at the sea-air interface. Uncertainties in the air-sea CO2 flux come not only from the gas exchange coefficient, but also from the ΔpCO2. The uncertainties mainly come from the poorly constrained estimates of the sea surface pCO2. Indeed the seasonal and geographical variation of surface water pCO2 is much greater (from 150 to 750 uatm) than that of the atmosphere, which varies by 20 uatm to around 370 uatm in remote uncontaminated marine air (Feely and al., 2001). OCVR-System : an innovative tool to improve pCO2sw estimation Oceanic Variables Climatology pC02 database Atmosphere state Raw data Assimilation module Systematic errors Network MLP-CLIM OCVR-System pCO2sw = Particular Event + Trend + Seasonal Figure 1: OCVR architecture used for a global ocean pCO2sw reanalysis from 1989 to 2009 at 2° resolution. Ocean pCO2 time series are one of the most valuable tools to observe trends of carbon fluxes. These analyses are limited by the coverage of measurements (less than 5% at 2° and monthly resolution over the last 20 years). The rapid development of satellite measurements which provide very large volumes of data (weekly) and high resolution (less than 1°) is an alternative to this problem. However the fluxes can only be obtained with indirect methods based either on numerical modelling, or from robust algorithms using observable drivers. The system OCVR belongs to this latter family. OCVR is a neural network framework developed by CLIMMOD within the CARBONES-EU FP7 project (see Fig. 1). As input variables, it uses observations from satellites (Surface Chlorophyll, Sea Surface Temperature...), in-situ and model outputs (Temperature, Salinity, Mixed Layer Depth,…) which control to first-order the surface ocean pCO2. A variational data assimilation scheme efficiently incorporates new sets of pCO2 observations (trend and seasonal adjustments), and takes into account extreme events like El Nino. The system then uses supplied atmospheric CO2 concentration to calculate air-sea flux according to a selectable exchange parameterization (e.g. Wanninkhof 1992, Nightingale 2000, Takahashi 2009). The results obtained with the OCVR-system are illustrated as global maps (see Fig. 2) and ocean time series (see Fig. 3). !"#$%&&%' !"#$%&&&' !"#$( ) ) &' Figure 2 : Global pCO2sw maps from OCVR. January simulations for 1990, 2000 and 2009. 2) Model policy The model has been developed by ClimMod partner and it is not freely available to the public. Any request on the model should be sent to: [email protected] [email protected] 3) References Feely, R.A., C.L. Sabine, T. Takahashi, and R. Wanninkhof (2001) : Uptake and storage of carbon dioxide in the oceans: The global CO2 survey. Oceanography, 14(4), 18–32. Nightingale, P.D., Malin, G., Law, C.S., Watson, A.J., Liss, P.S., Liddicoat, M.I., Boutin, J., UpsillGoddard, R.C., 2000. In situ evaluation of air-sea gas exchange parameterizations using novel conservative and volatile tracers. Glob. Biogeochem Cycles 14, 373–387. Sabine, CL, RA Feely, N. Gruber, R. M. Key, K. Lee, J. L. Bullister, R. Wanninkhof, C. S. Wong, D.W.R. Wallace, B. Tilbrook, FJ Millero, T.-H. Peng, A. Kozyr, T. Ono and AF Rios (2004): The oceanic sink for anthropogenic CO2. Science, 305 (5682), 367-371. Taro Takahashi, Stewart C. Sutherland, Rik Wanninkhof, Colm Sweeney, Richard A. Feely, David W. Chipman, Burke Hales, Gernot Friederich, Francisco Chavez, Christopher Sabine, Andrew Watson, Dorothee C.E. Bakker, Ute Schuster, Nicolas Metzl, Hisayuki Yoshikawa-Inoue, Masao Ishii, Takashi Midorikawa, Yukihiro Nojiri, Arne Körtzinger, Tobias Steinhoff, et al. Corrigendum to “Climatological mean and decadal change in surface ocean pCO2, and net sea–air CO2 flux over the global oceans” [Deep Sea Res. II 56 (2009) 554–577]. Wanninkhof, R., 1992. Relationship between wind speed and gas exchange. J. Geophys. Res. 97, 7373–7382.